1. Field of the Invention
The present invention relates to radio frequency (r.f.) amplifiers and, more particularly, to television r.f. amplifiers having separate composite video and synchronization (sync) amplification including means for selectively adding the amplified r.f. signal together.
2. Description of the Background Art
Radio frequency (r.f.) power amplification is often performed using a klystron although it is alternatively possible to employ a relatively large number of solid state amplifiers. In either case, the amplifiers must be proportioned to accepted the whole composite video r.f. signal from peak white to sync pulse bottom (FIG. 1), white being represented by zero amplitude, black being represented by approximately 60% of peak amplitude, and the bottom of the sync pulses being represented by the peak amplitude itself. Thus, the picture content is in the bottom half of the power range of the amplifier, with the top being used to provide only sync pulses. This means that the amplifier is only in the upper half of its power range for 7% of the time, which is a very inefficient way to use its overall power capability.